There is another Bitcoin forum called witcoin and they have implemented an interesting system: You have to pay bitcoins to post and cast votes, and you get a revenue share on replies and upvotes.
That is probably taking it a bit too far for a "general public" site, but how about allowing optional donations for good answers by encouraging everyone to associate their profile with a Bitcoin receiving address?
The same idea was brought up on Stackoverflow (with Flattr), where it was received very negatively. But I think on a Bitcoin site, such a system would be very topical. And of course, it is opt-in on both ends (for receiving and paying).
And to those who oppose the idea of encouraging or supporting this behaviour, would you be offended if people gave a receiving address on their profile anyway?
Or is this even against the Terms of Service here?